Vapor generator



y 1957 P. M. DOELL ETAL 3,320,934

VA POR GENERATOR Filed April 5, 1965 FIG! mVENToRs Dayld E. James BYPh|||p M. Doell ATTORNEY United States Patent 3,320,934 VAPOR GENERATORPhilip M. Doell, Wadsworth, and David E. James, Barberton, Ohio,assiguors to The Babcock & Wilcox Company, New York, N.Y., a corporationof New Jersey Filed Apr. 5, 1965, Ser. No. 445,658 6 Claims. (Cl.122-406) The present invention relates in general to the constructionand operation of a forced flow fluid heating unit and more particularlyto improvements in the construction and arrangement of fluid heatingcircuits especially adapted for use in a forced circulation once-throughvapor generating and superheating unit.

The general object of the present invention is the provision of a fluidheating unit of the character described so constructed and arranged asto assure an optimum distribution of fluid to all fluid flow paths andto assure an optimum relationship of fluid velocity within the tubes toheat input into the tube walls to effect adequate cooling of the tubewalls to a safe temperature without imposing an excessive pressure dropin the fluid flow path.

A further and more specific object of the invention is improvement inthe construction and arrangement of fluid heating circuits of a forcedflow vapor generator of the type described in US. Patent No. 3,081,748,issued to Paul H. Koch, wherein the vapor generator is fired by aplurality of cyclone furnaces. Specifically, the invention is directedto the provision of fluid flow circuitry in a unit of the characterdescribed permitting by-passing of a portion of the fluid around thefluid heating circuitry of the cyclone furnaces during operation in theupper part of the load range without overheating the tubes of thecyclone furnaces, thus realizing an appreciable decrease in pressuredrop in the fluid flow path and a corresponding reduction in the feedpump cost and power requirements.

The various features of novelty which characterize our invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which we have illustrated and described a preferred embodimentof the invention.

FIG. 1 is a sectional elevation of a once-through forced flow steamgenerator embodying the invention;

FIG. 2 is a partial sectional view taken along the line .2-2 of FIG. 1.

In the drawings the invention has been illustrated as embodied in aforced flow once-through steam generator intended for central stationuse. The particular unit illustrated is designed to produce a maximumcontinuous steam output of 3,840,000 lbs/hour at a pressure of 3600p.s.i.g. and a total temperature of 1000 F. at the superr heater outlet,based on feedwater being supplied at a temperature of 548 F., withprovisions for reheating the steam.

The main portions of the unit illustrated include an upright furnacechamber 10 of substantially rectangular horizontal cross section definedby front wall 11, rear wall 13, side walls 14, a roof 16 and a floor 17and having a gas outlet 18 at its upper end opening to a horizontallyextending gas pass 19 of rectangular vertical cross section formed by afloor 21 and extensions of the furnace roof 16 and side Walls 14. Gaspass 19 communicates at its rear end with the upper end of an uprightgas passage 22 of rectangular horizontal cross section formed by a frontwall 23, a rear wall 24, side walls 26 and an extension of the roof ofthe gas pass 19.

The fuel firing section comprises independently operable horizontallyextending cyclone type furnaces 27 of relatively small volume andboundary wall area disposed on opposite walls 11 and 13 at the lowerportion of the furnace chamber 10. Each cyclone furnace is arranged toburn solid fuel at high rates of heat release and separately dischargehigh temperature gaseous products of combustion and separated ashresidue as a molten slag into the lower portion of the chamber 10. Floor17 is formed with suit able openings, not shown, for the discharge ofmolten slag to a slag tank, not shown.

Gas pass 19 is occupied by a secondary superheater 28, a high pressurereheater section 29 and a low pressure reheater 31 arranged in serieswith respect to gas flow; while gas pass 22 is occupied in the directionof gas flow by a high pressure reheater section 32, a primarysuperheater 33 and an econ-omizer 34.

In the normal operation of the fluid heating unit, combustion air and arelatively coarse crushed fuel is supplied to the cyclone furnaces fromindependently controllable sources and the fuel is burned in the cyclonefurnaces at high rates of heat release suflicient to maintain a normalmean temperature therein above the fuel-ash fusion temperature. Ashseparates as a molten slag which flows into the lower portion of thechamber 10 and is discharged to the slag tank, while gases with arelatively small amount of slag particles in suspension discharge intothe lower portion of the chamber 10. The heating gases then flowupwardly through chamber 10 to the outlet 18 of gas pass 19, thenpasssuccessively over and between the tubes of secondary superheater 28,reheater 29, and reheater 31 in gas pass 19 and over and between thetubes of reheater 32, primary superheater 33 and economizer 34 in gaspass 22, and then discharge to another heat trap, not shown, beforeflowing to the stack. It will be understood that in accord ance withwell-known practice, each of the superheater and reheater sectionsextends across the full width of its corresponding gas pass and isformed for serial flow by multiple looped tubes.

Feedwater at high pressure is supplied by feed pump, not shown, toeconomizer inlet header 25, then passes through economizer 34 to outletheader 30 from which it flows through a downcomer 35 to the cyclonefurnace fluid heating circuits. Each cyclone furnace has its boundarywalls lined or formed by tube panels constructed and arranged in amanner similar to that described in the aforesaid US. Patent No.3,081,748. The high pressure fluid from the downcorner 35 flows inparallel to cyclone furnace supply headers iii by way of supply tubes45, each one of the parallel flow streams passing through thecircumferential wall tubes of the corresponding cyclone furnace to adischarge header S0. Streams of fluid discharging from headers 50 arecollected in a conduit 36 for flow to the fluid heating circuitry offurnace chamber 10.

Each of the upright boundary walls of furnace 10 is lined by upwardlyextending parallel tubes so arranged as to provide three passes offluid. Thus front wall 11 comprises initial upflow tubes 37A, secondupflow tubes 37B disposed in the spaces between and contiguous toinitial upflow tubes 37A, and third upflow tubes 37C. Rear wall 13includes initial upflow tubes 38A, second upflow tubes 38B situated inthe spaces between and contiguous to tubes 358A, and third upflow tubes38C forming a screen extending through gas pass 19. Each side wall 14has initial upflow tubes 39A, second upflow tubes 3913 located in thespaces between and contiguous to tubes 39A, and third upflow tubes 39C.Rear wall tubes 38A, 383 have their upper portions bent inwardly andupwardly and then rearwardly and upwardly to form a nose arch 41. Floor17 is lined by a row of tubes 42 ex tending between an inlet header 43and an outlet header 44, with header 43 being arranged for supply offluid from conduit 36 and header 44 being connected by a conduit as fordischarge of fluid to a ring shaped header a high pressure turbine, notshown.

3 47 extending about and outside of the lower end of furnace and adaptedto supply fluid to initial upflow tubes 37A, 38A and 39A of furnace 10.

The initial upflow tubes of the front, rear and side walls of furnace 10have their outlet ends connected to a ring shaped header 49 extendingabout and outside of furnace 10 at about the level of nose arch 41.Fluid passing through initial upflow tubes 37A, 38A and 39A is collectedin header 49 and then passed through a conduit 51 to a ring shapedheader 52 disposed about and outside of furnace 10 at around the levelof floor 17 and arranged to supply fluid to second upflow tubes 37B, 38Band 39B. The second upflow tubes of the front, rear and side Walls offurnace 10 extend from the floor 17 to about the level of nose arch 41and have their upper ends connected to headers 53, 54 and 56,respectively.

Third pass upflow tubes 37C, 38C and 39C extend from the level of nosearch 41 to the top of the furnace, tubes 37C extending between inlet andoutlet headers 57 and 58, tubes 38C between inlet and outlet headers 59and 61, and tubes 39C between inlet and outlet headers 62 and 63, withheaders 57, 59 and 62 being respectively connected for supply of fluidfrom headers 53, 54 and 56. Outlet headers 58, 61 and 63 are connectedfor flow of fluid to a header 66 which is arranged to distribute thefluid to tubes 67 forming the roof of furnace 10 and gas passes 19 and22 and having their discharge ends connected to a header 68. From header68 the fluid flows through a conduit 69 for distribution to boundarywall tubes of gas passes 19 and 22.

Each of the upright boundary walls of gas passes 19 and 22 includesupright parallel tubes, front wall 23 having tubes 71 extending betweeninlet and outlet headers 72 and 73, rear wall 24 having tubes 74extending between inlet and outlet headers 76 and 77, each side wall 26having tubes 78 extending between inlet and outlet headers 79 and 81,-and each side wall of gas pass 19 having tubes 82 extending betweeninlet and outlet headers 83 and 84. Floor 21 is lined by a row of tubes86 having their inlet ends connected to headers S7 and their outlet endsto headers 73, with headers '73 being connected for flow of fluid toheaders 88 by a row of screen tubes 89. Headers 72, 76, 79, 83 and .87are connected for parallel supply of fluid from conduit 69, whileheaders 77, $1, 84 and 98 are arranged for discharge to a commoncollection header 91 from which fluid passes to the primary superheater3 3 by way of a conduit 92.

Thus in operation up to a predetermined partial load the high pressurefluid supplied by the feed pump passes through economizer 34; then flowsin parallel through the fluid heating circuits of cyclone furnaces 27then passes through floor tubes 42; then flows upwardly in parallelthrough the radiant heat absorbing initial upflow tubes of the frontrear and side walls of the furnace to collecting header 49; then passesin parallel upflow through the second upflow tubes 37B, 38B and 39B ofthe furnace; then in parallel through third upflow tubes 37C, 38C and39C; then through tubes 6'7 forming the roof of furnace 10 and gaspasses 19 and 22; then in parallel upflow through convection heatabsorbing tubes of the upright boundary walls of gas pass 22 and theside and floor boundaries of gas pass 19; then successively passesthrough primary superheater 33 and secondary superheater 28 to Partiallyexpanded steam from the turbine successively passes through reheatersections 32 and 29 to and through an intermediate pressure turbine, notshown, then flows through reheater 31 to a low pressure turbine, notshown, wherein final expansion takes place.

In accordance with the invention, during operation throughout the upperpart of the load range of the vapor generator a portion of the fluidflowing through the downcomer is by-passed around the flow circuitry ofthe cyclone furnaces 27 and around floor tubes 42 by means of a conduit94 connecting downcomer 35 and header 44, with conduit 94 being providedwith a fluid flow control valve 96. Valve 96' always remains closed atlow loads and during start-ups. When a predetermined partial load isreached valve 96 may be opened manually, or may be opened automaticallywith the controlling impulse coming from an indicator of the load on thevapor generator, such as by an impulse generator or controller 95 whichautomatically and continuously measures the rate of fluid flow inconduit 35 and translates any deviation from some preset minimum valueof rate of fluid flow into an impulse force change which is transmittedto valve 96 by way of line 95A to actuate the valve. By-pass valve 96may be operated in a number of ways. It may be operated to maintain thepressure drop of the fluid due to flow through the circuitry of cyclonefurnaces 2'7 and floor tubes 42 substantially constant from thepredetermined partial load to full load. It may be operated in responseto variations in load in such a manner as to have a given opening at agiven load. It may also be completely opened at the predeterminedpartial load and maintained in this position to full load, in which casethe pressure drop across the cyclone furnace flow circuitry and floortubes 42 immediately sharply decreases at a predetermined partial loadand then gradually increases as the load increases. By any of thesemodes of valve operation, the pressure drop across the cyclone furnacefluid heating circuitry and floor tubes 42 will be considerably lessthroughout the operative load range of valve 96- than the pressure dropthat would exist without by-passing fluid around such circuitry, therebyproviding a corresponding reduction in the feed pump cost and powerrequirements.

A cyclone furnace is characterized by a nearly constant heat absorptionrate (B.t.u./hr./ft. over its operative load range. In the presentembodiment the cyclone furnace tube metals are designed for apredetermined partial load, about one-third of a full load. Since thecyclone furnaces have a substantially constant heat absorption rate overtheir operative load range and since the cyclone metals are set by onethird load conditions, it is possible to by-pass fluid around thecyclone fluid heating circuitry throughout the upper part of the loadrange without overheating tubes of that circuitry, thus affording amarked reduction in pressure drop through such circuitry in the upperpart of the load range. Similarly, the tube metals of floor 17 aredesigned for a predetermined partial load and have a substantiallyconstant heat absorption rate over the load range because they areprotected by a slag covering. So it is possible also to by-pass fluidaround floor tubes 42 in the upper part of the load range withoutoverheating such tubes, thereby providing a further reduction in fluidpressure drop.

By way of example, and not of limitation, in a commercial embodiment ofthe invention, valve 96 is designed to by-pass a portion of the fluidflowing through downcomer 35 around the flow circuitry of cyclonefurnaces 27 and floor tubes 42 at loads above 55 percent of full load.As the load increases, the flow through conduit 35 increases causingimpulse generator 95 to automatically transmit an impulse by way of line95A to actuate valve 96 such that flow in excess of 55 percent of fullload up to percent of full load is by-passed through conduit 94, whileflow rate through the cyclone furnace fluid heating circuitry and tubes42 is maintained substantially constant. Valve 96 is at its maximum openposition at 85 percent full load, so that flow through the cyclonefurnace fluid heating circuitary and tubes 42 gradually increases as theload increases beyond 85 percent full load. Immediately before valve 96opens on increasing load beyond 55 percent full load, the pressure dropacross the cyclone furnace fluid heating circuitry and tubes 42 is about45 p.s.i. When the valve 96 opens the pressure drop remainssubstantially constant up to 85 percent load and then graduallyincresases to a full load value of 50 psi, which is about one-quarter ofthe pressure drop which would exist at full load without by-passingfluid around such circuitry.

What is claimed is:

1. In a forced circulation fluid heating unit, walls including fluidheating tubes forming a furnace chamber having a gas outlet, wallsincluding fluid heating tubes forming a combustion chamber of circularcross'section having a gas outlet opening to said furnace chamber,

means for burning fuel at high rates of heat release in said combustionchamber, means for supplying a vaporizable fluid to said combustionchamber wall tubes, means connecting said combustion chamber wall tubesfor serial flow of fluid to said furnace chamber wall tubes, and meansfor maintaining the pressure drop of the fluid due to flow through saidcombustion chamber Wall tubes substantially constant from full load to apredetermined partial load, said last named means including means forby-passing a portion of the fluid inflow to said combustion chamber walltubes to said furnace wall tubes, and means responsive to variations intotal rate of fluid flow to said combustion chamber wall tubes forincreasing the rate of flow of fluid by-passing said combustion chamberwall tubes as the load increases beyond said predetermined partial load.

2. In a forced flow vapor generating and superheating unit having wallsforming a gas flow path, a combustion chamber of circular cross-sectionsupplying heating gases to said gas flow path, a once-through fluid flowpath arranged to receive a vaporizable fluid at one end and dischargesuperheated vapor at its opposite end and including a first fluidheating section lining the walls of said combustion chamber and a secondfluid heating section in said gas flow path connected for series flow offluid from said first fluid heating section, and a valve-controlledconduit around said first fluid heating section, the method of operatingsaid unit which comprises passing all of the fluid entering said fluidflow path successively through said first and second fluid heatingsections in the lower part of the load range, and regulating theresistance of fluid flow through said first fluid heating section in theupper part of the load range by by-passing a portion of the fluid inflowto the first section through said conduit to a position downstream ofthe fluid outflow side of said first section.

3. A once-through forced circulation vapor generator comprising wallsincluding radiant heat absorbing fluid heating tubes defining an uprightfurnace chamber having a heating gas outlet, means including convectionheat absorbing fluid heating tubes forming a gas pass serially connectedto said gas outlet, at bank of vapor superheating tubes positioned insaid gas pass in the path of gas flow, walls including fluid heatingtubes forming a combustion chamber of circular cross-section having agas outlet opening to said furnace chamber, means for burning fuel athigh rates of heat release in said combustion chamber, means forsupplying a vaporizable fluid to said combustion chamber wall tubes, andmeans for interconnecting said fluid heating tubes and vaporsuper-heating tubes to provide a serial flow of fluid successivelythrough the combustion chamber wall t-ubes, some of the radiant heatabsorbing fluid heating tubes of each of said furnace chamber walls, theremaining radiant heat absorbing fluid heating tubes of said furnacechamber walls, the convection heat absorbing fluid heating tubes, andthe bank of vapor superheating tubes.

4. A once-through forced circulation generator comprising wallsincluding radiant heat absorbing fluid heating tubes defining an uprightfurnace chamber having a heating gas outlet, means including convectionheat absorbing fluid heating tubes forming a gas pass serially connectedto said gas outlet, at bank of vapor superheating tubes positioned insaid gas pass in the path of gas flow, Walls including fluid heatingtubes forming a combustion chamber of circular cross-section having agas outlet opening to said furnace chamber, means for burning fuel athigh rates of heat release in said combustion chamber, means forsupplying a vaporizable fluid to said combustion chamber wall tubes andmeans for interconnecting said fluid heating tubes and vapor superheating tubes to provide a serial flow of fluid successively through thecombustion chamber wall tubes, alternate radiant heat absorbing fluidheating tubes of each of said furnace chamber Walls, the remainingradiant heat absorbing fluid heating tubes of said furnace chamberwalls, the convection heat absorbing fluid heating tubes, and the bankof vapor superheating tubes.

5. In a forced circulation fluid heating unit, walls including fluidheating tubes forming a furnace chamber having a gas outlet, wallsincluding fluid heating tubes forming a combustion chamber of circularcrosssection having a gas outlet opening to said furnace chamber, meansfor burning fuel at high rates of heat release in said combustion,chamber, means for supplying a vaporizable fluid to said combustionchamber Wall tubes, means connecting said combustion chamber Wall tubesfor serial flow of fluid to said furnace chamber Wall tubes, and meansfor regulating the pressure drop of the fluid due to flow through saidcombustion chamber wall tubes from full load to a predetermined partialload, said last named means including means for bypassing a portion ofthe fluid inflow to said combustion chamber Wall tubes to said furnaceWall tubes, and means responsive to variations in total rate of fluidflow to said combustion chamber wall tubes for varying the rate of flowof fluid by-passing said combustion chamber 'Wall tubes as the loadincreases beyond said predetermined partial load.

6. In a forced circulation fluid heating unit, walls including fluidheating tubes forming a furnace chamber having a gas outlet, wallsincluding fluid heating tubes forming a combustion chamber of circularcrosssection having a gas outlet opening to said furnace chamber, meansfor burning fuel at high rates of heat release in said combustionchamber, means for supplying a vaporizable fluid to said combustionchamber wall tubes, said combustion chamber having a nearly constantheat absorption rate over its operative load range, means connectingsaid combustion chamber wall tubes for serial flow of fluid to saidfurnace chamber wall tubes, and means for regulating the pressure dropof the fluid due to flow through said combustion chamber wall tubes fromfull load to a predetermined partial load, said last named meansincluding means for bypassing a portion of the fluid inflow to saidcombustion chamber wall tubes to said furnace wall tubes, and meansresponsive to variations in total rate of fluid flow to said combustionchamber wall tubes for varying the rate of flow of fluid by-passing saidcombustion chamber Wall tubes as the load increases beyond saidpredetermined partial load.

References Cited by the Examiner UNITED STATES PATENTS 3,033,177 5/ 1962Koch et a1. 122-235 3,081,748 3/1963 Koch 122-406 3,135,251 6/ 1964 Kane122406 FOREIGN PATENTS 912,029 12/ 1962 Great Britain.

CHARLES J. MYHRE, Primary Examiner.

1. IN A FORCED CIRCULATION FLUID HEATING UNIT, WALLS INCLUDING FLUIDHEATING TUBES FORMING A FURNACE CHAMBER HAVING A GAS OUTLET, WALLSINCLUDING FLUID HEATING TUBES FORMING A COMBUSTION CHAMBER OF CIRCULARCROSS-SECTION HAVING A GAS OUTLET OPENING TO SAID FURNACE CHAMBER, MEANSFOR BURNING FUEL AT HIGH RATES OF HEAT RELEASE IN SAID COMBUSTIONCHAMBER, MEANS FOR SUPPLYING A VAPORIZABLE FLUID TO SAID COMBUSTIONCHAMBER WALL TUBES, MEANS CONNECTING SAID COMBUSTION CHAMBER WALL TUBESFOR SERIAL FLOW OF FLUID TO SAID FURNACE CHAMBER WALL TUBES, AND MEANSFOR MAINTAINING THE PRESSURE DROP OF THE FLUID DUE TO FLOW THROUGH SAIDCOMBUSTION CHAMBER WALL TUBES SUBSTANTIALLY CONSTANT FROM FULL LOAD TO APREDETERMINED PARTIAL LOAD, SAID LAST NAMED MEANS INCLUDING MEANS FORBY-PASSING A PORTION OF THE FLUID INFLOW TO SAID COMBUSTION CHAMBER WALLTUBES TO SAID FURNACE WALL TUBES, AND MEANS RESPONSIVE TO VARIATIONS INTOTAL RATE OF FLUID FLOW TO SAID COMBUSTION CHAMBER WALL TUBES FORINCREAS-